The present invention relates generally to dampers, and more particularly to a damper piston assembly having a having a rod and a piston.
Conventional dampers include dampers having a cylinder containing a damping fluid (such as oil) and having a damper piston assembly including a piston which slideably engages the cylinder. The fluid passes through an orifice of a valve assembly of the piston. Valve assemblies include those having a disk located adjacent the orifice and covering the orifice. Fluid is forced through the orifice when the pressure of the fluid urges the disk away from the orifice. Valve assemblies include those having a compression orifice and a compression disk and a separate rebound orifice and a separate rebound disk. A rod has a first end attached to the piston and a second end extending outside the cylinder. The cylinder and the rod are attached to separate structures to dampen relative motion of the two structures along the direction of piston travel.
In some conventional dampers, the first end of the rod extends through the piston. The first end of the rod has external threads, and a nut is threadably engaged on the first end of the rod to secure the piston longitudinally between the nut and a shoulder of the rod. Typically, the tightened nut exerts a force of generally 2,500 pounds (plus or minus several hundred pounds) on the piston including the valve assembly and including the compression and rebound disks of the valve assembly. However, although the torque applied to the nut can be reasonably controlled, because of thread variations of the nut and tolerances in the parts of the valve assembly, the force on the piston (and on the valve assembly and on the compression and rebound disks) can vary greatly by several hundred pounds from damper to damper.
In other conventional dampers, one end of the piston is welded to the first end of the rod, the valve assembly is positioned in the piston, and the other end of the piston is crimped to retain the valve assembly.
What is needed is a damper piston assembly which is convenient to make and which exerts less force on the piston including the valve assembly.
In a first expression of a first embodiment of the invention, a damper piston assembly includes a rod, a piston, a rivet disk, and a spring. The rod has a longitudinal axis, a riveted end, and a longitudinal stop. The piston surrounds the rod between the riveted end and the longitudinal stop. The piston includes a valve assembly having a valve body with an orifice extending therethrough. The rivet disk surrounds the rod and has an opening for fluid communication with the orifice. The rivet disk is longitudinally secured between the piston and the riveted end of the rod. The spring is positioned in compression longitudinally between the rivet disk and the longitudinal stop of the rod. In one example, the spring is a Belleville washer.
In a second expression of a first embodiment of the invention, a damper includes a tube and a damper piston assembly. The tube contains a damping fluid. The damper piston assembly includes a rod, a piston, a rivet disk, and a spring. The rod has a longitudinal axis, a riveted end, and a longitudinal stop. The piston is located within, and is slidingly engageable with, the tube. The piston surrounds the rod between the riveted end and the longitudinal stop. The piston includes a valve assembly having a valve body with an orifice extending therethrough. The rivet disk has a hole for fluid communication with the orifice. The rivet disk is longitudinally secured between the piston and the riveted end of the rod. The spring is positioned in compression longitudinally between the rivet disk and the longitudinal stop of the rod. In one example, the spring is a Belleville washer.
One method for making a damper piston assembly includes steps a) through h). Step a) includes providing a rod having a longitudinal axis, a first end, and a longitudinal stop. Step b) includes providing a piston including a valve assembly having a valve body with an orifice extending therethrough and with a mounting hole extending therethrough. Step c) includes mounting the piston on the rod with the first end of the rod extending through the mounting hole of the valve body. Step d) includes mounting a spring on the rod. Step e) includes providing a rivet disk having a mounting hole extending therethrough and having an opening extending therethrough for fluid communication with the orifice. Step f) includes mounting the rivet disk on the rod, after mounting the piston and the spring on the rod. Step g) includes longitudinally moving the rivet disk against the piston compressing the spring with the first end of the rod extending through the mounting hole of the rivet disk. Step h) includes, after step g), peening the first end of the rod against the rivet disk to define a riveted end of the rod. In one example of the first method, step d) is performed after step c), the spring in a relaxed state extends beyond the piston, and there is also included the step of measuring, after step d) and before step f), the force required to compress the spring flush with the piston, and the step, before step f), of mounting a shim disk, as needed, on the rod, wherein the thickness of the shim disk is chosen so that, after step f), the spring exerts a predetermined force.
Several benefits and advantages are derived from the invention. The spring and rivet attachment of the piston (including the valve assembly) to the rod provides a secure attachment with a lower clamp load on the piston (including the valve assembly). A lower clamp load on the valve assembly means less damage to valve components and especially to orifice disks (for those valve assemblies having orifice disks). In one example, the clamp load is generally 250 pounds. The spring and rivet attachment also provides a more precise and repeatable clamp load on the piston (including the valve assembly) regardless of the manufacturing tolerances of the individual components, especially in the example when a shim disk is employed. Having an exact and repeatable clamp load for each manufactured damper piston assembly provides for optimal valve operation (such as optimal orifice disk operation for those valve assemblies having orifice disks). The spring and rivet attachment reduces costs by eliminating the threaded rod of conventional piston assemblies employing threaded rods and simplifies and reduces the costs of assembly equipment compared to conventional weld and crimp or conventional threaded-nut assembly equipment.